[Elecraft] attenuator in amp was Re: K3 and Expert 1K-FA

[dave.wilburn at gmail.com]

When the K3 came out there was a big deal about the default ALC polarity that resulted in a mod. Will the default connections of the KPA500 work with an un-moded radio or will we need the mod?

David Wilburn
NM4M 
Sent from my Verizon Wireless BlackBerry

-----Original Message-----
From: Doug Faunt N6TQS +1-510-655-8604 <faunt at panix.com>
Date: Wed, 21 Apr 2010 14:00:02 
To: <d.cutter at ntlworld.com>
Cc: <elecraft at mailman.qth.net>
Subject: Re: [Elecraft] attenuator in amp was Re:  K3 and Expert 1K-FA

Probably the biggest issue is getting rid of the 70 watts of added
heat.  If there's someplace in the exiting airstream to put these
resistors.... 

73, doug

   From: "David Cutter" <d.cutter at ntlworld.com>
   Date: Wed, 21 Apr 2010 18:54:21 +0100

   T0-220 style power film resistors are fairly cheap and can easily be mounted 
   on heat-sinking surfaces.

   David
   G3UNA


   > Hm, I wonder if the KPA500 has or can have provision for this.  That
   > amp can be driven to full output by 30 watts or so, IIRC.  With the K3
   > (or K2), power control could be done automatically by having the amp
   > tell the radio that it's active over the serial interface, but it's
   > clear the KPA500 has much provision for being used with radios other
   > than the K3.
   >
   > 73, doug
   >
   Tom W8JI wrote:
   >
   >   > The correct approach would be an
   >   > attenuator pad so the radio could run at near full power and
   >   > not have a chance of overdriving the amp, ...
   >
   >   I don't understand why more people don't do that.  For example, a 3 dB
   >   attenuator between the transceiver and amplifier ensures that a 100W
   >   exciter won't overdrive an amplifier that requires 50W of drive.  The 3
   >   dB loss on receive is hardly ever an issue but if you're worried about
   >   it, just put the attenuator inside the amplifier, after the T/R relay.
   >
   >   Seems like a simple, foolproof solution.
   >
   > 

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